Hand-held power tool with antivibration mount

ABSTRACT

A hand-held power tool comprises an internal combustion engine on which a power tool is mounted and by which it is driven. The engine is mounted by vibration isolators on an essentially rigid supporting structure comprising a base portion, a front handle and a rear handle. Four vibration isolators are so arranged as to isolate the supporting structure from vibration of the engine while providing effective control of the tool by an operator holding the supporting structure by the front and rear handles. The vibration isolators are shown in the form of hollow barrelshaped bodies of elastomeric material.

D United States Ptent [151 3,637,029 Sherwood, Jr, et a1. 1 1 Jan. 25,1972 [54] HAND-HELD POWER TUQL WITH 3,224,473 12/1965 Dobbertin et al...173/162 X ANTIVIBRATION MUUNT 3,372,718 3/1968 lrgens ...l73/162 X3,409,056 11/1968 Rauh ...l73/l62 X [72] Inventors: Noble P. Sherwood,Jr., Greenwich; James 3,542,095 1 1/1970 Frederickson et a1. ..173/162 XP. Strickland, Fairlield, both of Conn.

- Primary Examiner-David H. Brown {73] Asslgnee Textmn ProvldenceAtt0rneyR0bert E. Burns and Emmanuel .l. Lobato [22] Filed: Sept. 14,1970 7 AB R T [21] Appl. No.: 71,829 [5 1 ST Ac A hand-held power toolcomprises an internal combustion engine on which a power tool is mountedand by which it is fi 13 2 7 driven. The engine is mounted by vibrationisolators on an essentially rigid supporting structure comprising a baseportion, [58] Field of Search "173/1621 248/9; 143/32 R a front handleand a rear handle. Four vibration isolators are so arranged as toisolate the supporting structure from vibra- [56] References cued tionof the engine while providing effective control of the tool UMTED STATESPATENTS by an operator holding the supporting structure by the front andrear handles. The v1brat|on nsolators are shown in the 2,538,954 1/1951Efromson et al ..248/9 form of hollow barrel-shaped bodies ofelastomeric material. 2,894,489 7 1959 Clay 1 ..173/162 3,139,152 6/1964Bager ..248/9 x 13 919M514 Drawmg Flgures HAND-HELD POWER TOOL WITHANTIVIBRATION MIOUNT The present invention relates to engine-drivenhand-held power tools and in particular to tools powered by smallinternal combustion engines. While the invention is herein illustratedand described with reference to a chain saw, it will be understood thatit is applicable to other hand-held power tools.

Chain saws and other hand-held power tools are commonly driven by asmall light weight internal combustion engine normally operating at aspeed of over 5,000 r.p.m. The chain saw cutter bar or other tool iscommonly mounted on an engine chassis and the latter is provided withsuitable handles by means of which the engine and tool are held andmanipulated by an operator.

A small engine of the kind used for hand-held power tools unavoidablygenerates vibration. This is particularly true of small two-cyclesingle-cylinder internal combustion engines operating at high speed. Thevibration of the engine transmitted through the handles to the operatorhas been found to cause early fatigue and, in some instances, numbnessof the arms. The operators control of the tool is thereby impaired, thuscreating a safety hazard. Moreover, continued use of the power tool overan extended period of time may cause serious impairment of the operatorshealth.

It has been proposed to reduce the vibration transmitted to the operatorby providing vibration isolators between the handles and the engine.However, vibration isolators having a sufficiently soft action to beeffective in reducing transmission of vibration to the handles permitrelative movement between the handles and the tool and hence make itimpossible for the operator to control the tool effectively.

It is an object of the present invention to attenuate the vibrationtransmitted by a chain saw or other engine-driven power tool to theoperator while, at the same time, providing the operator with precisecontrol of the tool at all times. In accordance with the invention, theengine is mounted by means of vibration isolators on an essentiallyrigid supporting structure having front and rear handles by which thetool is held. The isolators are so arranged as to isolate the supportingstructure from the vibration of the engine while providing asufficiently firm connection between the supporting structure and theengine to afford precise control of the tool mounted on, and driven by,the engine.

In an illustrated embodiment of the invention, the vibration isolatorsby means of which the engine is mounted on the supporting structurecomprise hollow barrel-shaped bodies of elastomeric material having anannular circumferential groove midway between opposite ends. Thevibration isolators are mounted between the engine and the supportingstructure by cooperating mounting fixtures one of which engages oppositeends of the barrel-shaped body while the other comprises a ring seatedin the circumferential groove. A pin extending through the barrel-shapedbody and the ring provides a failsafe feature in that, even if theelastomer body fails, the pin of one fixture extends through the ringportion of the other fixture and thus provides a secure connectionbetween the engine and the supporting structure.

The vibration isolators have the characteristic of being stiffer in onedirection and more flexible in a direction perpendicular thereto. Byselectively arranging the isolators with respect to the principal modeof vibration of the engine, it has been found possible to isolate theengine from the supporting structure while, at the same time, providinga sufficiently firm connection between the supporting structure and theengine to afford adequate control of the tool by the operator.

The objects and advantages of the invention will be more fullyunderstood from the following description of a preferred embodiment ofthe invention shown by way of example in the drawings, in which:

FIG. 1 is a side view of a chain saw in accordance with the invention,the engine being shown in phantom and portions being broken away inorder to show more clearly the mounting of the vibration isolators;

FIG. 2 is a front elevation of the chain saw with the engine and cutterbar shown in phantom and with portions broken away and shown in section;

FIG. 3 is a plan view of the supporting structure with the engineremoved; and

FIG. 4 is a perspective view of one-half of a vibration isolator shownpartially in section.

A hand-held power tool in accordance with the present invention is shownby way of example in the drawings as a chain saw having an engine 10driving a saw chain 11 running on a guide bar 12 which is mounted on theright-hand side of the engine by means of studs and nuts 13 and projectsforwardly. The engine 10 is shown as a single-cylinder two-stroke-cycleinternal combustion engine having a crankshaft the axis of which ishorizontal when the engine is in a normal upright position, as shown inFIG. 1, and extends transversely of the engine in line with the sprocketby which the chain 11 is driven. The engine cylinder extends: rearwardlyfrom the crankshaft and is approximately horizontal although it may besomewhat inclined. The engine is air-cooled and is constructed largelyof light weight metals and alloys in order to minimize the weight of thechain saw. It is designed to run at relatively high speeds, for examplespeeds in the range of 5,000 to 8,000 r.p.m.

Although the crankshaft is counterbalanced, the engine developsvibration, particularly when operating at high speed. The principal modeof vibration is in a fore-and-aft direction because of the reciprocationof the engine piston. There are other modes of vibration due, forexample, to the rotation of the crankshaft and the throw of the:connecting rod. The center of vibration is approximately at theintersection of the axes of the cylinder and the crankshaft. Because ofthe cutter bar being mounted on the right side of the engine, the centerof mass of the engine saw assembly is laterally offset from the centerof vibration. This results in the generation of a couple producing anoscillatory vibration of the engine.

If handles for holding and manipulating the chain saw were afixeddirectly on the engine chassis in. accordance with prior practice, thevibration of the engine would be transmitted to the operator with theill effects referredl to above. However, in accordance with theinvention, the handles are not secured on the chassis but are part of a,supporting structure on which the engine is mounted by means ofvibration isolators so as to isolate the vibration of the engine fromthe handles.

In the embodiment illustrated in the drawings, the supporting structurecomprises a base portion 15, a front handle 16 and a rear handle 17. Thebase portion 15 is generally triangular with a transversely extendingforward portion 15a and two rearwardly converging side portions 15b and15c which, in cross section, are preferably of channel or I-beam sectionin order to provide strength and stiffness with minimum weight. Theweight of the structure is further reduced by openings 15d.

The front handle 16 is shown formed of tubular stock which is shaped toprovide an upwardly extending side portion 16a and a horizontal topportion 16b joined by an inclined portion 160. The lower end of the sideportion 16a fits over an upwardly projecting portion 15c provided at theforward lefthand comer of the base and is secured by transverselyextending pins or rivets 18. The tubing forming the handle 16 is ofsufficient weight and diameter, for example 1 /4 inch, as to beessentially rigid. The front handle preferably slopes somewhatrearwardly, as seen in FIG. 1, so that the upper horizontal portion 16bis located above the front end portion of the engine.

The rear handle 17 is somewhat Dshaped with an upwardly extendingforward portion 17, a downwardly inclined pistol grip portion 17b and alower guard portion 17c. Suitable engine controls are associated withthe rear handle, including a trigger 19 controlling the throttle of theengine and a throttle lock button 20 which is pressed inwardly whenstarting the engine. While the rear handle 17 may be made as a separatemember and rigidly secured to the base portion 15, it is shown as beingintegral with the base portion. Thus, the supporting structurecomprising the base portion 15, front handle 16 and rear handle 17constitute a unitary structure which is essentially rigid so as to avoidobjectionable flexing under the forces imposed on it in use.

The engine is mounted on the supporting structure comprising the baseportion and handles 16 and 17 by four vibration isolators 21, 22, 23 and24. The vibration isolators are so selected and so located as to provideeffective isolation between the engine and the supporting structurewhile at the same time affording the operator full control of the chainsaw. While spring or other types of vibration isolators can be used ifdesired, the vibration isolators shown by way of example in the drawingsare hollow barrel-shaped bodies of elastomeric material having metalwashers 25 set in opposite ends. The isolators may be molded as completeunits or may be made in two halves, one of which is illustrated in FIG.4. Reduced end surfaces 21a of the halves are then bonded together, forexample adhesively or by vulcanizing, so as to form a completebarrel-shaped body with an annular circumferential groove 21b midwaybetween the ends. It will be seen that each half of the isolator isapproximately frustoconical. The maximum diameter is, for example, 40percent greater than the minimum diameter and the wall thickness is, forexample, approximately percent of the minimum diameter. The overalllength is, for example, about 65 percent greater than the minimumdiameter and hence somewhat greater than the maximum diameter of theisolator. The material from which the isolator is formed is anelastomeric material, for example a natural or synthetic rubbercompound, e.g., polyurethane, having a suitable durometer value. For thewall thickness and proportions shown by way of example in the drawings,the durometer value is between and 55 and preferably between and 45. Ifthe material is not itself resistant to oil, gas or other fluidhydrocarbons, the isolator is provided with an outer layer or coating ofelastomeric material having such resistance.

Each of the vibration isolators is mounted by means of a first fixtureengaging its opposite ends and a second fixture having a ring portionreceived in the annular circumferential groove 21b of the isolator. Theindividual vibration isolators are mounted in selected locations andselected positions to provide good vibration isolation between theengine and the supporting structure while, at the same time, affordingthe operator effective control of the position of the engine and henceof the cutting bar of the chain saw. The configuration of the isolatorsis such that they are stiffer in the direction of their longitudinalaxis and more flexible in a direction perpendicular to the axis.Preferably, the flexibility of the isolator is approximately twice asgreat in a transverse direction as in the direction of the central axis.

The vibration isolator 21 supporting the engine at its rear is disposedvertically between spaced portions 17d and 17s of the rear handle 17engaging opposite ends of the isolator. A fixture 27 having a ringportion received in the central circumferential groove of the isolatoris integral with, or secured on, the lower rear end portion of theengine chassis which is thereby supported by the vibration isolator 21.A pin 28 extends axially through the vibration isolator 21 and throughaligned holes in the supporting portions 17d and 17e. it will be seenthat, even if the vibration isolator should fail, the rear end portionof the engine is still captured by reason of the pin 28 passing throughthe ring portion of the fixture 27 on the engine chassis.

The second vibration isolator 22 is located at the front of the engineand is positioned with its axis horizontal and approximately parallel tothe crankshaft. The opposite ends of the vibration isolator 22 areengaged by spaced portions 15f and 15g of the base portion 15. Thecircumferential groove of the vibration isolator is engaged by a ringportion 30a of a fixture 30 secured to the bottom of the engine near thefront in suitable manner, for example by screws 3011. A pin 31 extendsaxially through the isolator 22 and through aligned holes in thesupporting portions 15f and 15g.

The third vibration isolator 23 is located at the front of the engine onthe lower left-hand side and is positioned with its axis vertical.Opposite ends of the isolator are engaged by spaced portions 15h and 15:of the base 15. A pin 32 extends axially through the isolator and isreceived in aligned holes in the portions 1511 and 151' of the base. Aring portion 30c of the fixture 30 is received in the circumferentialgroove midway between the ends of the isolator 23.

The fourth vibration isolator 24 is located at the front of the engineand on the upper right-hand side and is positioned with its axisapproximately horizontal and parallel to the crankshaft of the engine.Opposite ends of the isolator are engaged by portions 33a and 33b of afixture 33 suitably secured to the engine chassis, for example by screws34. A pin 35 extends axially through the vibration isolator 24 andthrough aligned holes in the opposite portions 33a and 33b of thefixture 33. The circumferential groove of the vibration isolator 24 isengaged by a ring portion 36a of a fixture 36 which fits into the upperright-hand portion of the front handle 16 and is suitably secured, forexample by a pin 37.

The space between the portions which engage opposite ends of each of theisolators, for example the portions 17d and 17e engaging opposite endsof the isolator 21, are spaced apart a distance less than the overalllength of the isolator when in unconfined condition so that the isolatoris compressed in an axial direction when it is placed between thesupporting surfaces engaging its opposite ends. For example, an isolatorwhich in uncompressed condition is 1.31 inches long is compressedbetween the supporting surfaces to 1.25 inches. The vibration isolatoris sufficiently compressible circumferentially to permit the isolator tobe drawn into the ring portion of the central support, for example thering 27 with respect to the isolator 21, prior to the isolator beingcompressed in an axial direction. The ring thereupon snaps into thecentral circumferential groove of the isolator. When the isolator isconfined in an axial direction, it is no longer compressiblecircumferentially and hence the ring is securely held in thecircumferential groove of the isolator.

It will be seen that the four vibration isolators supporting the engine10 are located at the apices of a tetrahedron. Three of the isolatorsare located at the front of the engine with two of them below the engineand at opposite sides while the third is located above the engine and atone side. The fourth vibration isolator 21 is located at the rear of theengine. Two of the vibration isolators, namely isolators 22 and 24, arepositioned with their axis approximately horizontal and parallel withthe crankshaft of the engine while the other two isolators, 21 and 23,are positioned with their axes vertical. It will be noted that in allinstances the axes of the isolators are perpendicular to a fore-and-aftdirection and hence approximately perpendicular to the axis of theengine cylinder. By reason of the isolators having a higher springconstant in a direction axial of the isolator and a lower springconstant in a direction perpendicular to the axis, and by reason of thelocation and positioning of the isolators as described, the transmissionof engine vibration to the supporting structure comprising the front andrear handles is effectively attenuated. However, an operator holding thechain saw by the front and rear handles has effective control of thechain saw and can accurately position the cutter bar both vertically andlaterally.

While a preferred embodiment of the invention has been illustrated byway of example in the drawings and is herein particularly described, itwill be understood that the invention is in no way limited to thisembodiment.

What we claim and desire to secure by letters patent is:

1. An engine-driven hand-held power tool comprising an engine having afront portion and a rear portion, a tool mounted on and driven by saidengine, an engine-supporting structure comprising a base portion, afront handle and a rear handle, said base portion and handlesconstituting a unitary essentially rigid structure, and means mountingsaid engine on said supporting structure comprising three vibrationisolators supporting the front portion of said engine on said supportingstructure and a fourth vibration isolator supporting the rear portion ofsaid engine on said supporting structure, said vibration isolators beingarranged to isolate said supporting structure from vibration of saidengine while providing control of said tool by an operator holding saidsupporting structure by said handles.

2. An engine-driven hand-held power tool according to claim l, in whicheach of said isolators is stiffer in the direction of a central axis andmore yielding in a direction perpendicular to said axis.

3. An engine-driven hand-held power tool according to claim 2, in whichsaid isolator supporting the rear portion of the engine and at least oneof the isolators supporting the front portion of the engine have theirsaid axes approximately vertical in a normal operating position of saidpower tool.

4. An engine-driven hand-held power tool according to claim 3, in whichtwo of said isolators supporting the front portion of said engine havesaid axis horizontal.

5. An engine-driven hand-held power tool comprising an engine having afront portion and a rear portion, an operating tool mounted on anddriven by said engine, an engine-supporting structure comprising a fronthandle, a rear handle and a connecting portion, said handles andconnecting portion constituting a unitary essentially rigid structure,and means mounting said engine on said supporting structure comprising aplurality of vibration isolators and associated mounting means on saidsupporting structure and said engine respectively, each of saidisolators comprising a hollow barrel-shaped body of elastomeric materialhaving opposite ends and an annular circumferential groove between saidends, said mounting means comprising respectively a support havingportions engaging opposite ends of said isolator and a ring received insaid annular groove.

6. An engine-driven hand-held power tool according to claim 5, in whichat least the exposed outer surface of said elastomeric material isresistant to fluid hydrocarbons.

7. An engine-driven hand-held power tool according to claim 5, in whichsaid elastomeric body is in a compressed condition between said portionsof the support engaging opposite ends of said body.

8. An engine-driven hand-held power tool according to claim 5, in whicha pin connecting said portions engaging opposite ends of said bodyextends axially through said body and through said ring.

9. An engine-driven hand-held power tool according to claim 5, in whichsaid engine has a crankshaft arranged horizontally and transversely anda cylinder arranged with a central axis extending in an approximatelyfore-and-aft direction, and in which said mounting means comprises threeof said isolators at the front portion of the engine and a fourth saidisolator at the rear portion of the engine, two of said isolators at thefront portion of the engine being arranged with central axesapproximately parallel to said crankshaft, and the third said isolatorat the front portion of the engine and said isolator at the rear portionof the engine being arranged with central axes approximately vertical.

110. An engine-driven hand-held power tool according to claim 5, inwhich said elastomeric material has a durometer value of between 35 and55.

11. An engine-driven hand-held power tool according to claim 10, inwhich the durometer value of said elastomeric material is between 40 and45.

12. An engine-driven hand-held power tool according to claim 5, in whichsaid mounting means comprises three of said isolators supporting thefront portion of the engine and a fourth said isolator supporting therear portion of said engine on said supporting structure.

13. An engine-driven hand-held power tool according to claim 12, inwhich said isolator at the rear portion of the engine and one of saidisolators at the front portion of the engine are arranged with a centralaxis of the isolator vertical.

1. An engine-driven hand-held power tool comprising an engine having afront portion and a rear portion, a tool mounted on and driven by saidengine, an engine-supporting structure comprising a base portion, afront handle and a rear handle, said base portion and handlesconstituting a unitary essentially rigid structure, and means mountingsaid engine on said supporting structure comprising three vibrationisolators supporting the front portion of said engine on said supportingstructure and a fourth vibration isolator supporting the rear portion ofsaid engine on said supporting structure, said vibration isolators beingarranged to isolate said supporting structure from vibration of saidengine while providing control of said tool by an operator holding saidsupporting structure by said handles.
 2. An engine-driven hand-heldpower tool according to claim 1, in which each of said isolators isstiffer in the direction of a central axis and more yielding in adirection perpendicular to said axis.
 3. An engine-driven hand-heldpower tool according to claim 2, in which said isolator supporting therear portion of the engine and at least one of the isolators supportingthe front portion of the engine have their said axes approximatelyvertical in a normal operating position of said power tool.
 4. Anengine-driven hand-held power tool according to claim 3, in which two ofsaid isolators supporting the front portion of said engine have saidaxis horizontal.
 5. An engine-driven hand-held power tool comprising anengine having a front portion and a rear portion, an operating toolmounted on and driven by said engine, an engine-supporting structurecomprising a front handle, a rear handle and a connecting portion, saidhandles and connecting portion constituting a unitary essentially riGidstructure, and means mounting said engine on said supporting structurecomprising a plurality of vibration isolators and associated mountingmeans on said supporting structure and said engine respectively, each ofsaid isolators comprising a hollow barrel-shaped body of elastomericmaterial having opposite ends and an annular circumferential groovebetween said ends, said mounting means comprising respectively a supporthaving portions engaging opposite ends of said isolator and a ringreceived in said annular groove.
 6. An engine-driven hand-held powertool according to claim 5, in which at least the exposed outer surfaceof said elastomeric material is resistant to fluid hydrocarbons.
 7. Anengine-driven hand-held power tool according to claim 5, in which saidelastomeric body is in a compressed condition between said portions ofthe support engaging opposite ends of said body.
 8. An engine-drivenhand-held power tool according to claim 5, in which a pin connectingsaid portions engaging opposite ends of said body extends axiallythrough said body and through said ring.
 9. An engine-driven hand-heldpower tool according to claim 5, in which said engine has a crankshaftarranged horizontally and transversely and a cylinder arranged with acentral axis extending in an approximately fore-and-aft direction, andin which said mounting means comprises three of said isolators at thefront portion of the engine and a fourth said isolator at the rearportion of the engine, two of said isolators at the front portion of theengine being arranged with central axes approximately parallel to saidcrankshaft, and the third said isolator at the front portion of theengine and said isolator at the rear portion of the engine beingarranged with central axes approximately vertical.
 10. An engine-drivenhand-held power tool according to claim 5, in which said elastomericmaterial has a durometer value of between 35 and
 55. 11. Anengine-driven hand-held power tool according to claim 10, in which thedurometer value of said elastomeric material is between 40 and
 45. 12.An engine-driven hand-held power tool according to claim 5, in whichsaid mounting means comprises three of said isolators supporting thefront portion of the engine and a fourth said isolator supporting therear portion of said engine on said supporting structure.
 13. Anengine-driven hand-held power tool according to claim 12, in which saidisolator at the rear portion of the engine and one of said isolators atthe front portion of the engine are arranged with a central axis of theisolator vertical.